Sending device with signal voltage converter



June 18,

MOI IOOII 040i SOUNDING DEVICE WITH SIGNAL VOLTAGE CONVERTER C402 .25MFD.

Original Filed April 10, 1964 T402 R406 a 2Nl67| I ossol 4E50-8 mo:

26 D402 R407 R403 IN207OA 5.6K

a T404 C404 I zms'n .25MFD 200v 0403 l .25MFD 400v TR4OI 2 J E SD R5MARK 6V OPEN 0 Or SPACE ov CLOSE LO'DP -6 l4 -1 l m RECEIVE TELEOPSONEC'Rcun. I L DATA TEL PROCESSING EXCHANGE SEND EQUIPMENT IIIIII} CIRCUITfir INVENTOR JAMES TI NEISWINTER CARL N PEDERSOW ATTORNEYS United StatesPatent 3,389,223 SENDING DEVICE WITH SIGNAL VOLTAGE CONVERTER James T.Neiswinter, Garden City, N.Y., and Carl N. Pederson, Westmont, Ill.,assignors to The Pioneer Electric and Research Corporation, Forest Park,Ill. Original application Apr. 10, 1964, Ser. No. 358,739. Divided andthis application Oct. 20, 1967, Ser. No.

9 Claims. (Cl. 178-17) ABSTRACT OF THE DISCLOSURE A signal voltageconverter circuit for connecting between data communication equipmentoperable at low voltage levels and transmission lines normally operableat high voltages. The low voltage output signals from the datacommunication equipment are utilized to control an electronic switchingcircuit to key a higher voltage telegraph loop. The electronic switchincludes a Shockley diode and the current carrying terminals of asilicon controlled rectifier in series across input terminals of atelegraph loop. The converter includes two circuits which generatealternating voltage control signals representing line control and signaltransmission bit conditions, one of which circuits applies controlpulses to extinguish the Shockley diode to accomplish quick extinctionof current conduction through the silicon controlled rectifier toelectronically key the loop to open. The other circuit applies controlpulses of sufiicient potential level to the control terminal of thesilicon controlled rectifier to cause the rectifier to fire and key theloop to closed. A Request Send circuit in the converter renders the loopopen control circuit subject to being biased inoperative whenever theloop closed control circuit is rendered operative by data bittransmission.

Cross-reference to related application This application is a division ofapplication Ser. No. 358,739, filed Apr. 10, 1964.

Background of the invention The present invention relates to signalconverters which may be used as interface between a low voltage datatransmitting and receiving device, such as a business machine, and ahigh voltage telegraph loop as is normally supplied by telephone ortelegraph companies, and more particularly to a novel circuitarrangement for use at the location of a business machine as the sendcircuit so that the business machine may communicate directly to aconventional telecommunication line.

The signal voltage on the telegraph loop is comparatively high, andusually 130 or 260 volts, with a current flow of about 60 ma. for themark condition and zero current for the space condition. Normally,batteries are provided by a central oflice, a fixed load resistance ispresent at the receiver station and a suitable keyer is provided at thesend station to generate the. mark signal voltage by closing thetelegraph loop and the space signal by opening the loop circuit. A marksignal is conventionally produced by closing the circuit so that thebattery voltageis impressed across the load resistance and a spacesignal is characterized by an open circuit in timed relation to thestart pulse.

On the other hand, business machines customarily operate withcomparatively low signal voltages. The E. I. A. (Electronic IndustryAssociation) standard specifies a negative voltage of between -3 and--20 for a mark and between about +3 and +20 for a space, with a lowcurrent flowing for one or both conditions. In some cases a businessmachine may use the negative voltages for 3,389,223 Patented June 18,1968 'ice Summary of the invention The principal object of the presentinvention is to provide an improved interface or signal voltageconverter for use with comparatively low signal voltage equipment suchas business machines to thereby adapt such equipment'to send overconventional telephone or telegraph lines .using their customarycomparatively high voltage signals.

The send circuit converts the low voltage business machine signals tothe high voltage telegraph loop signals. The power supply, whichfurnishes the voltages required for the operation of the transistors,may be of any suitable type, and forms no part of the present invention.

Other objects of the invention are to provide:

(1) a novel send circuit employing a silicon controlled rectifier (SCR)together with a Shockley diode for effecting the keying of the telegraphloop;

(2) a novel send circuit having alternating voltage generators forapplying repeated control voltages to the SOR in the send circuit tomaintain it in the desired conductive or non-conductive condition; and

(3) alternating voltage generating circuits employing unijunctiontransistors that are readily controlled by transistor circuitsresponsive to the comparatively low level signals produced by the dataprocessing equipment.

Brief description of the drawings These and other objects of theinvention will become more fully apparent from the claims, and from thedescription as it proceeds in connection with the appended drawingswherein:

FIGURE 1 is a block diagram showing the novel signal converter of thepresent invention at a location ad-' Description 0 the disclosedembodiment Referring now to FIGURE 1 of the drawings, the presentinvention is incorporated within the block 9 representing the signalconverter of a communications system utilizing a pair of transmissionlines 12 and 13 that are connected through a telephone or telegraphexchange 14 to a further piece of data processing equipment (not shown)containing a sending circuit and receiving circuit which may beidentical to that of blocks 9 and 16. At the local station, normally atclose proximity to the signal converter 9 of the present invention,there is a business machine 16 that operates with input data receivedfrom transmission line 12 and which may send out data over transmissionline 13.

The overall function of the sender circuit of FIGURE 2 is that for aninput voltage of about 6 volts on the SD (Send Data) terminal 5 from thebusiness machine, this circuit will close the telegraph loop throughtransmission line 13 and exchange 14 connected to its output terminals 8and 10 so that 60 ma. flows, and for an input of about zero volts itwill open the telegraph loop so that no current flows.

An additional fiun'ction is that for 'a voltage of about zero on its RS(Request Send) terminal. 3, it will hold the telegraph loop open; andfor la voltage of about -6 volts on terminal 3, this circuit will .closethe loop as far as this part of the circuit is concerned, 'and the markand space voltages on the SD terminal 5 will then control the conditionof the loop.

In the idle condition of the business machine on the sending side, aboutzero volts is applied to the base terminals of both transistor T405 andtransistor T406 and both are thereby biased so as to be non-conducting.

Transistor T404 is a unijunction transistor and has volts on its base 1.It will therefore require a voltage on its emitter more positive thanabout 8 volts to fire it.

On the basis that the base 1 to base 2 resistance of unijunctiontransistor T404, when nonconducting, is about 10,000 ohms, the 20 voltson its base 1 will appear through resistor R407 to the emitter as about16 volts, which is not sufiiciently positive relative to base voltage 20to fire the unijunction. Unijunction transistor T404 is thereforenormally non conducting.

The current from the 20 volts connection to base 1 will flow through theunijunction, and through resistor R406 (and the base to emitter path oftransistor T403, to make transistor T403 normally conducting.

With transistor T403 conducting, near zero voltage is applied throughresistor R404 to base 2 of a second unijunction transistor T403 and viaa parallel path through resistor R403 to capacitor C402 and the emitterof unijunction transistor T402. Base 1 of unijunction transistor T403 isconnected to 20 volts.

When capacitor C402 charges in a positive direction to about -8 volts,unijunction transistor T402 will fire and quickly discharge C402.

C402 will continue .to charge slowly and discharge quickly so long asthe near zero voltage is applied to resistors R403 and R404.

In the marking condition the telegraph loop may have ma. flowing in itwhich flows through a silicon controlled rectifier (SCR) T401, and aShockley diode DS401 which for purposes of this description are assumedto be fired at this time.

Each time the unijunction transistor T402 fires to discharge C402, alarge negative pulse is applied to the junction between Shockley diodeDS401 and an ordinary diode D401.

This large negative pulse momentarily diverts the current normallyflowing in the loop circuit from the central office through resist-orR401, idiode D401, Shockley diode DS401, SCR T401 and resistor R402 backtoward the central ofiice, so that the current flows through C402.Therefore, both Shockley diode DS401 and SCR T 401 are left with littleor no forward current. This condition I causes both of these lastmentioned components to cease conducting.

Shockley diode DS401 will cease conducting sooner than SCR T401, as itrequires a shorter negative pulse, which is why it is used in thecircuit; and with Shockley diode DS401 nonconducting, SCR T401 mustbecome then non-conducting. The SCR T401 does not begin conducting until.a positive going signal is applied to its con trol element 26.

Therefore, to review, wit-h about zero volts applied to both the SDterminal 5 and RS terminal 3, unijunction transistor T402 will oscillateland the negative going discharge pulses applied through capacitor C402to the telegraph loop will extinguish both Shockley diode DS401 and SCRT401 and cause the loop current to become zero.

One pulse through capacitor C402 would be sufficient to make the loopcurrent zero. However, if, after the current had become zero, some straypulse should refire SCR T401, the loop would go marking even though thebusiness machine remained as sending a space. The purpose of thecontinuous stream of negative pulses all during the spacing condition ofthe business machine is so that if a stray pulse should fire the SCRT401, the next negative pulse from capacitor C402 would extinguish itagain and only an extremely short marking pulse would be applied to theloop.

When SCR T401 does fire, a high negative going change is created at thejunction of Shockley diode DS401 and capacitor C402. Diode D402 is forthe purpose of diverting this negative pulse :away from the emitter ofunijunction transistor T402 so that it is not dam-aged.

Diode D401 is for the purpose of preventing damage to unijunctiontransistor T402 in case the plus and minus volts batteries applied atthe central office to the tip and ring of the telegraph loop are appliedin the wrong direction.

When -6 volts is applied to the RS (Request Send) terminal 3, transistorT405 goes conducting and applies about zero volts to the emitter oftransistor T406. Transistor T406 remains non-conducting because of aboutzero voltage on its base.

When -6 volts for a mark is applied to the SD (Send data) terminal 5,transistor T406 goes conducting and about zero volts is applied toresistors R408, R407 and R406 through lead 24.

The near zero volts on resistor R406 together with the +6.8 voltsthrough resistor R405 causes transistor T403 to go non-conducting.Unijunction transistor T402 then stops from oscillating.

The near zero volts on resistors R407 and R408 in combination withcapacitor C404 cause unijunction transistor T404 to start oscillating ata frequency, preferably in the audio frequency range.

This audio frequency signal is transmitted through transformer TR401 andcreates positive and negative voltage on its secondary, the positivepulses of which. fire SCR T401. This causes Shockley diode DS401 to fireand the loop accordingly becomes closed and the 60 ma. marking currentflows.

Again, only one pulse is necessary to close the loop, but if only onepulse were used, a momentary opening of the loop at the central officeor any other place, due to testing or rearrangements, would extinguishboth SCR T401 and Shockley diode DS401 and the loop would remain open.The continuous stream of pulses that reach the control grid of SCR T401during the marking condition of the business machine assure that, afterany external opening of the loop which would extinguish SCR T401 will befired again as soon as the external open of the loop is removed.

Capacitor C401 is for the purpose of slowing down the build up ofvoltage across Shockley diode DS401 and SCR T401 when the loop is openedso that these components are not refired by this voltage. If a relaywith considerable inductance is in series with the loop, the inductivekick caused by stopping the current in this relay may cause a refiringof the SCR land the circuit would oscillate due to this condition.

The remaining components not specifically mentioned are used in theirnormal manner well-known to those skilled in this art, and furtherdiscussion is therefore deemed unnecessary.

The phase alternating voltage signal as used in the claims is intendedto cover all types of non-steady voltage signals including outputsignals from circuits such as, but not limited to, multi-vibrators whichmay be square waves and from the circuits here employing unijunctiontransistors which may have a saw-tooth or other configuration.

From the foregoing, it is apparent that there is provided by the presentinvention an interface or buffer unit uniquely adapted for connection toa piece of ofiice data processing equipment to enable it to senddirectly the comparatively high marking and spacing signal voltagespresent on a conventional telephone or telegraph line. The invention maybe embodied in other specific forms without departing from the spirit oressential characteristics thereof. The present embodiment is thereforeto be considered in all respects as illustrative and not restrictive,the scope of the invention being indicated by the appended claims ratherthan by the foregoing description, and all changes which come Within themeaning and range of equivalency of the claims are therefore intended tobe embraced therein.

What is claimed and desired to be secured by United States LettersPatent is: i

1. A signal converter for keying a telegraph loop comprising atransmission line powered by batteries at a telecommunications exchangewith mark and space voltage signals in timed relation in accord withcorresponding comparatively low voltage output signals from dataprocessing equipment, said converter comprising: a pair of terminalsconnected to the transmission line so that when an electrical circuitbetween said terminals is closed, a telegraph loop is completed througha circuit including said transmission line and said central station; acircuit connected between said terminals containing in seriesrelationship a Shockley diode and a silicon controlled rectifier poledin the same direction with the positive current carrying terminals ofsaid silicon controlled rectifier connected between the negative currentcarrying terminal of said Shockley diode and one of said pair ofterminals, said Shockley diode being a diode which will cease conductingdue to a shorter negative current pulse than necessary to cause asilicon controlled rectifier to become non-conductive; a first circuitwhich when energized generates an alternating voltage signal; meansincluding a capacitor for applying said alternating voltage signal tothe positive current carrying terminal of said Shockley diode forrapidly opening the circuit between said terminals and for extinguishingcurrent conduction through said silicon controlled rectifier; a secondcircuit which when energized generates an alternating voltage signal;means for applying the signal from said second circuit to a controlelectrode on said silicon controlled rectifier to cause said siliconcontrolled rectifier to fire; biasing means for controlling said firstcircuit and said second circuit so that only one of said first andsecond circuits can be energized to produce its alternating voltagesignal at a time; and means including a transistor circuit which changesits conduction condition in response to a mark or space signal from saiddata processing equipment to thereby modify the bias circuit and controlenergization of said first and second circuits.

2. A signal converter as defined in claim 1 wherein said first circuitcontains a unijunction transistor having a base connected to a point ofreference potential together with a diode connected between said pointof reference potential and the capacitor connected to said Shockleydiode and poled so as to protect said unijunction transistor fromdamaging transient voltages.

3. A signal converter as defined in claim 2 wherein said second circuitfor generating an alternating voltage signal contains a unijunctiontransistor and a capacitor connected to oscillate at an audio frequency,and means for inductively coupling said audio frequency signal to thecontrol element of said silicon controlled rectifier.

4. A signal converter for keying a telegraph loop comprising atransmission line powered by batteries at a telecommunications exchangewith mark and space voltage signals in timed relation in accord withcorresponding comparatively low voltage output signals from dataprocessing equipment, said converter comprising:

a pair of terminals connected to the transmission line;

a circuit component connected in series with said terminals that has alow electrical impedance when in a conducting state, a high electricalimpedance when in a non-conducting state, and a control element forcausing the component to change from a non-conductive state to aconductive state;

means including a first circuit for continuously generating analternating voltage signal for applying a voltage to a point in thecircuit between one of said terminals and said circuit component forcausing the ii component to change from a conductive state to anon-conductive state; and

means responsive to mark and space input signals from said dataprocessing equipment to apply an actuating voltage to said controlelement and a disabling voltage signal to said alternating voltagegenerating means in response to reception of one of said input signals,and to apply an actuating voltage to said alternating voltage generatingmeans and a disabling voltage signal to said control element in responseto reception of the other of said input signals.

5. A signal converter as defined in claim 4 having:

an input circuit connected to receive said input signals from the dataprocessing equipment and responsive to change its conduction conditionin response to mark or space signals;

circuit means connected from said input circuit to said first circuitfor continuously generating an alternating voltage signal formaintaining said circuit component in its non-conducting state inresponse to a spacing signal;

a second circuit for continuously generating an alternating voltagesignal for connection to said control element; and

circuit means connected from said input circuit to said second circuitfor maintaining said circuit component in its conducting state inresponse to a marking signal.

6. A signal converter as defined in claim 5 wherein the first and secondcircuits for continuously generating an alternating voltage whenenergized each contain a capacitor alternately charged and dischargedthrough a circuit arrangement including a unijnnction and said circuitcomponent in an SCR.

7. In a keying circuit for sending a coded signal comprising marking andspacing voltage signals in timed relation through a transmission linepowered by batteries at a central station, a pair of terminals connectedto the transmission line so that when an electrical circuit between saidterminals is closed a telegraph loop is completed through a circuitincluding said transmission line and said central station; a circuitbetween said terminals comprising a silicon controlled rectifier havingits current carrying terminals connected in series with the currentcarrying circuit and poled to conduct, when fired, electrical currentsupplied through the transmission line; and a firing circuit for saidsilicon controlled rectifier comprising means for continuouslygenerating an alternating voltage signal during the time interval thatthe circuit between said terminals is to be closed, to thereby minimizethe length of any time increment when said circuit is inadvertentlyopened resulting from a non-conductive condition of said siliconcontrolled rectifier.

8. The keying circuit as defined in claim 7 wherein said circuit betweensaid terminals further comprises: a first diode for protecting saidsilicon controlled rectifier against damage in event of polarityreversal on said terminals; a second diode in series between the firstdiode and said silicon controlled rectifier to decrease the timeincrement necessary to extinguish current conduction through saidsilicon controlled rectifier; and means includinga capacitor forapplying an alternating voltage to the circuit at a junction betweensaid first and second diodes for extinguishing current conductionthrough said silicon controlled rectifier.

9. The keying circuit as defined in claim 8 wherein the means forapplying the alternating voltage to the junction includes a transistorand further comprising a unidirectional conducting device connectedbetween said capacitor and a point of reference potential and poled topass transient voltages appearing on said transmission and coupledthrough said capacitor to the power supply and thereby avoid damage tosaid transistor.

No references cited. THOMAS A. ROBINSON, Primary Examiner.

